Melatonin (N-acetyl-5-methyoxytryptamine) is a neurohormone secreted from the pineal gland. In mammals, including humans, melatonin is normally secreted in a circadian (or twenty-four hour) rhythm with blood levels of approximately 10 pg/ml during the daytime, with levels increasing to approximately 80-100 pg/ml during the nighttime. Peak secretion of melatonin occurs at around 2 AM. (Waldhauser, F. and Steger, H., PROCEEDINGS OF THE FIRST INTERNATIONAL CONGRESS ON MELATONIN IN HUMANS, pp. 179-191, Vienna, Austria, (Nov. 1985)). Studies have shown that secretion of melatonin is suppressed by bright light. (Lewy, A. J., et.. al., Science 210:1267-1269 (1980)).
Melatonin has a short biological half-life, and is rapidly metabolized by the liver. (Aldhous, M., et. al., Br. J. Clin. Pharm. 19:517-521 (1985)). Thus, doses up to 6.6 grams per day have been used to study the effects of melatonin in humans. Although, generally, no ill effects have been observed from the use of these very high doses, one recent study reports that ingestion of 300 mg of melatonin daily, for four months, resulted in inhibition of ovulation in women. (Bettie, C. G., et. al., J. Clin. Endocrin. Metabol. 74:108-117 (1992)).
No function has clearly been associated with melatonin in humans. In fact, lack of melatonin in humans has not been associated with any major abnormality. (Arendt, J., et. al., PHOTOPERIODISM, MELATONIN AND THE PINEAL, London, England (Ciba Foundation Symposium 117) pp. 266-283 (1985)).